Seismic exploration systems now employ long spreads of a plurality of geophone locations that are laid out along a survey line with many more such locations than the number of channels in a recording unit. Consequently, during the recording of individual seismic records the system makes use of a much lesser number of the geophone groups or locations than there are laid out along the spread. The procedure commonly employed for developing data to be used in common depth point compositing of records, is facilitated by using a so-called roll along switch in connection with the making of a series of recordings to be composited. Such as roll along switch has a rotary set of contacts that make circuit connections with the recording channels. Then, by rotation of the switch the circuit connections are made to successive ones of the geophone locations in a step by step manner as individual records are taken. Often this may be carried out automatically as a series of records are taken with the roll-along switch in successive positions. Consequently, the chances of misidentifying the geographic location of the source of seismic signals related to the connected channels of a given record are quite considerable. The misidentification would be as to the channels which were connected to particular ones of the geophone locations. Sources of error include such situations as the fact that the common depth point switch did not change position, or the location of a particular geophone position in the spread was not correct, or the position of the recording truck to which the various geophone positions are connected was in error.
Consequently it is an object of this invention to provide for an identification means that may be applied to a particular one of a plurality of geophone connections or locations in order to identify that specific location along a spread. It is particularly useful as a series of changed connections are made during the making of recordings.
Another object of the invention is to make use of a signal generator outside the range of useful seismic energies which may be applied to a particular one of a plurality of geophone locations along a seismic spread as laid out on a survey line. By means of that signal the the particular location may be identified on each record.